A.13.1 The defdetpred form

The syntax of this form is

(defdetpred <
name
> <
num args
> <
body
>)

which defines a simple predicate that just runs lisp code and doesn't have to unify any variables. Arguments are referenced with:
(special-arg
<argnum>
)
. The body succeeds by default, but if a failure case arises, use:
(detpred-fail
<name>
<num args>
)
.